1. Field of Invention
The invention relates to the field of video signal processing, and particularly to processing of non-standard video signals.
2. Description of Related Art
Conventional television video broadcast signals comply with certain industry standards, such as PAL, SECAM, and NTSC for proper reception by various commercial TV receivers. In some broadcast locations, however, so-called non-standard video signals arise and are thereby broadcasted, for example, due to improper broadcast equipment or signaling. In such non-standard situations, conventional or standard television receiver equipment may not function properly. Problems may arise, for example, when non-standard signaling results in broadcast of video signals having more or less number of horizontal lines than ordinarily specified for standard programming. Accordingly, there is need to address non-standard video signals.
The invention enables television reception and display of non-standard broadcast signals, particularly by converting non-standard signals to acceptable signals. One preferred scheme processes non-standard video signals to handle any extra or missing horizontal lines, by using a digital frequency synthesizer, such as a modulo or digital phase lock loop-type circuit, to change a clock output signal proportionately according to a difference determined by comparing standard video signal value with actual input signal line count value, such that the modified clock output signal serves as a clock input signal for the following circuit, which accepts standard video format. Another alternative scheme processes a non-standard video signal to handle improper odd-even field sequencing of broadcast video signal.